The present invention relates to battery management, and more particularly, to apparatus for managing batteries in a serially connected string.
On-line battery monitoring is becoming acceptable common practice within telecommunication power systems applications. A number of commercial products are currently available for such purposes. See, for example, E Gotaas & A Nettum; “Single Cell Battery Management Systems (BMS)”; Intelec 2000; Sep. 10-14 2000; Phoenix; USA; Paper 36.2; or A Anbuky, P Pascoe & P Hunter; “Knowledge Based VRLA Battery Monitoring & Health Assessment”; Intelec 2000; Sep. 10-14 2000; Phoenix; USA; Paper 36.1.
Known commercial products can provide advantages over conventional intermittent or offline monitoring. The approach to monitoring often is either based on centralised sensing and intelligence (see for example S Deshpando et al; “Intelligent Monitoring System Satisfies Customer Needs for Continuous Monitoring and Assurance on VRLA Batteries”; INTELEC, 1999) or distributed sensing and centralised intelligence organisation. Many of these products deal with a low level of information processing (e.g. smoothing and limit violation detection) while leaving the intelligent part to a human expert.
With the advancement of microelectronic technology, local sensing and intelligence is becoming feasible, allowing for distributed sensing and intelligence organisation. One further aspect that may require attention for low-energy batteries is the power required by the sensor to operate. Sensors are normally parasitic on the battery. Energy consumption can become noticeable when dealing with low ampere-hour batteries.
Goals for an advanced battery management system include: a) presenting timely information on battery reserved time upon mains failure; b) presenting timely information on battery remaining life; and c) maintaining safe battery operation (i.e., preserving battery life). These goals may be partially met by a central management unit or left to a human expert. The goal of life preservation generally involves charge management and control. An appropriate hardware device for interaction among a group of cells to facilitate individual cell current feeding and draining is desirable. An optimal solution preferably would determine the internal status of each cell and provide a facility to individually optimise each cell's float charge.
There may be a trade-off between cost and the functionality that is provided by additional electronics. An application specific integrated circuit (ASIC) solution presented by Scott (N Scott; “A single Integrated Circuit Approach to Real Capacity Estimation and Life Management of VRLA Batteries”; Intelec'01; Edinburgh International Conference Centre (EICC) UK; 14-18 Oct. 2001) may satisfy some of the above-described requirements. However, an optimal ASIC design may swing this equation in favour of functionality. A further known system is described in A Anbuky, Z Ma & S Sanders; “Distributed VRLA Battery Management Organisation with Provision for Embedded Internet Interface”; Intelec 2000; Sep. 10-14 2000; Phoenix; USA; Paper 37.2.